1. Field of the Invention
The present invention pertains to techniques for sealing cylindrical members to circumscribing conduits. More particularly, the present invention relates to well tools, such as well packers, for selectively sealing a tubing string, for example, to a surrounding well conduit such as provided by casing or well liner, and is suitable for use in high-temperature applications.
2. Description of Prior Art
Well packers and other downhole equipment may be exposed to high temperatures. For example, known secondary recovery techniques for producing hydrocarbons include certain thermal recovery operations. Such thermal recovery operations include fire flooding and steam injection. In the case of fire flooding, oil sand about the periphery of a high viscosity oil formation is ignited and the fire maintained by the injection of air through wells about the formation horizon. As the combustion front advances through the formation, the oil decreases in viscosity and increases in mobility, moving toward one or more producing wells communicating with the interior of the formation.
Steam may be injected into one or more injection wells to reduce the viscosity of formation oil which may then be removed by a producing well. Alternatively, steam may be circulated down a well through which the reduced-viscosity oil is produced, the oil being isolated from the steam within the well bore.
Where downhole equipment is subject to high temperatures, such as in the cases of fire flooding or steam injection, variations in the length of the equipment, and particularly the tubing string, due to wide-ranging temperature changes must be accommodated. U.S. Pat. No. 3,391,742 discloses a mechanically-set, retrievable well packer particularly applicable for high-temperature well operations. After the packer is set, the tubing string by which the packer is run in the well may be moved longitudinally relative to the outer packer assembly, which is sealed and anchored to the surrounding well conduit, without unseating the packer. A dual mandrel assembly provides the capability of circulating steam while producing hydrocarbons through the packer.